This study investigated the effects of inquiry-based instruction on preservice teachers' beliefs concerning learning science through inquiry and their performance to apply a scientific inquiry process. A case study design was used in the study and the data were collected through interviews, observations and written documents. Two preservice teachers with different experiences in their previous science education were selected. The preservice teachers learnt both science and scientific inquiry process through open inquiry activities. The results of the research show that past experiences of preservice teachers are effective on beliefs about learning science through inquiry. The open inquiry science activities which allow preservice teachers' making discussion, collaboration, and interaction were effective in developing their beliefs concerning learning science through inquiry and increasing their ability to apply a scientific inquiry process. The overall findings indicate that inquiry-based activities should frequently be a preferred instruction method in preservice teacher education.